1. Field of the Invention
The invention pertains to the field of stair construction. More particularly, the invention pertains to a modular stone stair system.
2. Description of Related Art
For the purposes of terminology in describing a stair, the xe2x80x9ctreadxe2x80x9d is the horizontal part of the stair on which a person walks. All of the treads on a given staircase are usually the same depth (xe2x80x9cdepthxe2x80x9d meaning horizontal dimension in the direction of travel on the staircase, xe2x80x9cwidthxe2x80x9d being a horizontal dimension across the stair, orthogonal to the depth, and xe2x80x9cheightxe2x80x9d or xe2x80x9cthicknessxe2x80x9d being a vertical dimension, with xe2x80x9crisexe2x80x9d being the vertical distance between the top of a tread and the top of the next tread). A xe2x80x9clandingxe2x80x9d is a deeper tread which is usually the topmost element in the stair, although it is possible to have a landing at intervals in a staircase, for design purposes. A xe2x80x9criserxe2x80x9d is the vertical element which is located between one tread and the next, and a xe2x80x9cstringerxe2x80x9d is a piece which runs depthwise from the back of the riser toward the back of the staircase.
Stone stairs have long been used leading up to a building or home, or along paths and at retaining walls. In the past, most stone stairs were custom made of large pieces of stone, cut to fit each stair, with the tread and riser and (sometimes the stringer) typically being the same piece (known as a xe2x80x9cheavy treadxe2x80x9d). In some cases an entire stair might be cut from one piece of stone. The pieces used are very heavy, weighing as much as 2200 lbs., requiring multiple people and/or heavy equipment to construct the staircases. Each stone piece must be hand cut, and a mason is needed to cement the stone pieces into place and lay a full foundation.
Therefore, an easy, less expensive stone stair system is needed that can be assembled on a prepared flat surface from standardized parts without the aid of a mason, large construction crews or heavy equipment, and which is stable for repeated use.
Modular stair systems are known, in which standardized pieces are assembled into a stair. These systems are made of concrete, which allows for shapes to be molded which would be impossible to form economically from stone, which is a natural product which must be cut.
For example, U.S. Pat. No. 2,672,045, discloses a step construction comprising grooved saddles or side supports and grooved steps assembled with the riser of one step slidably overlapping the rearward portion of the tread of the next lower step. A small amount of mortar is placed in the grooves to hold the steps in the assembly together. Each tread/riser section is continuous in width across the step, and the stringer sections (called xe2x80x9csaddlesxe2x80x9d) are xe2x80x9cLxe2x80x9d shaped or otherwise stepped to support the outside edges of each tread/riser combination.
Another example is U.S. Pat. No. 3,343,316, which discloses xe2x80x9cLxe2x80x9d shaped steps, where the long side of the xe2x80x9cLxe2x80x9d serves as tread and the short side is a riser. Holes are drilled through the tread and the riser to lineup all the sections and keep the stairs secured to one another. This system is built on rising ground, so there are no stringers, and is intended to be made of molded concrete. Similarly, U.S. Pat. No. 3,813,831 discloses a prefabricated concrete stair system with separate treads and risers, where the riser has a shelf to hold the edge of the next lower tread, and the tread is pinned to the top of the riser. No stringers are present in this system, and the system must be laid on a sloping surface with the risers sunk in holes with dry packing.
A fourth example is U.S. Pat. No. 5,479,746, which discloses a modular staircase system using flat modules and modules with differing numbers of vertical support of which are xe2x80x9cLxe2x80x9d, xe2x80x9cTxe2x80x9d, xe2x80x9cFxe2x80x9d, and xe2x80x9cExe2x80x9d shaped. As in the last two stair systems, this invention needs to be laid on sloping ground.
A modular stone stair system using a plurality of modules in the form of stringers, risers, treads and landings in standardized thicknesses and widths. The risers, landings (if any) and treads have different widths dependent upon the width of the stairs desired, with the treads and landing (if any) being of the full width of the stair, and the risers being a modular width such that each tread or landing is underlain by a plurality of risers. Each level of the stair has a plurality of stringers, abutting the back of the tread and riser and running to the back of the stair. The stringers vary in depth depending upon how many steps are to be present, such that each level, except the bottom, overlaps the tread and riser of the next lower level by a fixed amount. The system can easily be assembled by two people, using a shovel, a level, and a ruler, giving the homeowner or contractor the option of choosing threshold heights, widths, and landings with varying depths.